1. Technical Field
The present invention relates to a method and system for monitoring etching processes utilized in the field of electronic circuitry. In particular, the present invention relates to a method and system for measuring etch depth. More particularly, the present invention relates to measuring etch depth in real time during etching cycles. Still more particularly, the present invention relates to a method and system for tracking etch depth in real time to accurately determine the end-point of an etching cycle.
2. Description of the Related Art
Etching technology in general is a rapidly developing field. Etching techniques are widely used in the field microelectronics to erode selected portions of a surface in order to produce a desired pattern on substrate surfaces. The need for greater precision in the profile and depth of etch channels has created a need for a method of accurately measuring etch depth during a cycle in order to prevent over-or under-etching product materials. Etching techniques are commonly categorized as either being "wet" or "dry" etching methods. Wet etching utilizes liquid etchants which provide high selectivity to both substrate and masking layers. Wet etching processes are typically isotropic, meaning that they provide poor control of etch profile.
Dry etching utilizes the physical mechanism of sputtering to remove substrate material. The directional nature of dry etching results in anisotropic etching in which essentially vertical etch profiles are produced. Reactive ion etching is a dry etch process which combines chemical and physical mechanisms and hence offers both adequate selectivity and greater edge profile precision.
Since etching techniques are time-dependent processes, it is possible to determine the end-point solely as a function of time. However, the etching process is also a function of several variables which are not temporally uniform. These variables include etch chamber exposure to room ambient, chemical distribution within the system, gas flow rates, operator experience etc. The result is a lack of accuracy and uniformity among the etches in a single cycle and also a lack of reproducibility between cycles.
Due to extremely low error tolerances which characterize VLSI production, the dry etch techniques employed therein generally require highly precise and specialized end-point detection techniques. The most common of the techniques used to detect the end-point during etching processes utilized in VLSI production include: 1) optical emission spectroscopy; 2) laser interferometry; 3) direct visual observation of the etched surface through a viewing port; and 4) mass spectroscopy. A problem associated with these techniques is twofold: first, highly sophisticated peripheral equipment must be added to the etching tool apparatus; and second, these techniques utilize an extremely small scale of measurement to provide the necessary level of precision required for VLSI patterns. As a result, these techniques are simply not practicable in etching applications that measure etch depth on a much larger scale. One such application in which the abovementioned methods are ineffective and time etches are used instead, is the etching process used in the fabrication of magnetic reading and/or recording element and disk sliders.
The magnetic reading and/or recording element is generally encapsulated in a disk slider, which provides physical support for both the magnetic reading and/or recording element and the electrical connections between the magnetic reading and/or recording element and the remainder of the disk drive system. The disk slider also provides an air-bearing surface which permits the magnetic reading and/or recording element to "fly" in close proximity to the surface of the spinning disk. Several parameters which are controlled by the design of the disk slider affect the amount of information which may be stored on the disk. One is the distance between the magnetic reading and/or recording element imbedded in the disk slider and the surface of the disk. As this distance is reduced, the spatial density of binary information encoded on the disk may be increased. Another parameter which is critical to disk slider performance is the depth of the contours which are etched onto the disk sliders after they have been lapped.
Disk sliders, typically formed from a ceramic wafer, generally have bottom surfaces that form air-bearing surfaces capable of flying over the spinning disk. The magnetic reading and/or recording element is mounted within the disk slider, and extends down through a rail, terminating at the air-bearing surface of the rail. Both lapping and etching processes attempt to create a smooth air-bearing surface by removing material from the magnetic reading and/or recording element and rail surfaces. To form sliders with air-bearing surfaces that are precisely positioned relative to the structure of the magnetic reading and/or recording element, the lapping and etching processes must be closely controlled.
Currently, several techniques are utilized to monitor and control lapping processes. Among such techniques is the use of electrical lapping guides. This technique involves measuring the resistance of a sensor strip located on the substrate containing the magnetic transducer elements being lapped. The sensor strip is lapped along one dimension to the same extent as the magnetic transducer elements. The resistance of the sensor strip at any given time indicates the amount of material that has been removed from the element and hence the resistance is an indication of the final height of the transducer element being lapped.
As previously discussed, current disk slider etching processes often utilize time as a primary end-point detection parameter. Control of these etching processes has therefore not kept pace with the need for increased etch depth precision. As a result, a problem associated with etching techniques, particularly those used for larger scale applications, is that of detecting the end-point of an etching cycle accurately and uniformly. It is important that the end-point of an etching cycle be accurately determined to reduce over- and underetching thereby increasing yield and run-to-run reproducibility.
Based on the foregoing, it can be appreciated that a need exists for an improved method and system that would allow the operator of an etching device to accurately measure etch depth in real time. Such a method and system, if implemented, would be useful by enabling the etch tool operator to accurately terminate the etching process at the precise point in time at which the target etch depth has been attained.